Thermostat actuator blade assembly

ABSTRACT

An actuator for use in a thermostat assembly comprising a blade formed from multilayered thermally responsive material. The blade includes spaced side legs joined at one end to define a blade area for connection to a heat source and further includes a compensating leg extending transversely between the spaced ends of said side legs and defining a point of actuation between the side legs. Each side leg defines an active leg portion adapted to quickly deform in response to heat to move the point of actuation a predetermined distance from an initial position. The compensating leg is adapted to receive heat from the side legs and respond by deforming so as to return the actuating point a predetermined distance toward its initial position to thereby compensate for additional movement of the actuation point induced by heat saturation of the side legs.

United States Patent [72] Inventor Ernest N.Taylor 2,128,869 8/l938Winborne 337/378 00 2231 E. 67th St.. Chicago. Ill. 60649 Primary Emmmuflamld Broom: 23532 Assistant Examiner-Dewitt M. Morgan l C 1 H I H &Pnemed J y Attorney ume C ement ume Lee ABSTRAT= An actuator for use ina thermostat assembly [54] TunkMosTA-r ACTUATOR BLADE ASSEMBLYcomprising a blade formed from multilayered thermally 6 chum m Drum,Flss responsive material. The blade Includes spaced side legs i joinedat one end to define a blade area for connection to a [52] US. Cl337/379, heat source and f th indudes a compensating k8 unending337/1o|337/378 transversely between the spaced ends of said side legsand [5 I] Int. Cl l-l0lh 37/52 d fi i a Point f actuation between heside Each side [50] Field of 337/l0l. |eg d fi es an iv le portionadapted to quickly deform in 365; response to heat to move the point ofactuation a predeter- 73/353-5 mined distance from an initial position.The compensating leg is adapted to receive heat from the side legs andrespond by [56] cued deforming so as to return the actuating point apredetermined UNITED STATES PATENTS distance toward its initial positionto thereby compensate for 3,238,780 3/l966 Doyle 337/378 (X) additionalmovement of the actuation point induced by heat 3,22l,l 24 ll/l965Mertler 337/354 saturation ofthe side legs.

422 :08 2: no l0 6 j I I '5 |O0 mun. "2 i04 4224 I l 4 l a "8 i t l rtus 104 H 1112" I20 T1 |32 I04 A I 34 L |Q2 H L 30 TI-IERMOSTAT ACTUATORBLADE ASSEMBLY BACKGROUND AND GENERAL DESCRIPTION OF THE INVENTION Thisinvention relates generally to an improved tempera ture-controlleddevice and more particularly relates to an improved actuator blade foruse in thermostat assemblies.

As well known by those skilled in the art, many thermostat assemblies incurrent use have actuator blades which cause the thermostat to haveundesirable operating characteristics. For instance, a principal defectin current thermostats is the inability of the actuator blade to respondquickly to a change in the temperature of the medium, such as a heatingor cooling appliance, being controlled. Because of defects in theactuator blade design, most prior assemblies generally have been unableto closely control the application of heat to a medium withoutexperiencing a substantial temperature differential between heatingcycles.

Further, the designs of .many prior actuator blades have resulted in anundesirable lag between the time at which the medium being controlledreaches a desired temperature, and the time at which the thermostatresponds by either cutting off the application of heat, if the medium isa heating appliance, or beginning the application of heat, if the mediumis a cooling appliance. This temperature overshoot or undershoot isparticularly prevalent in the first cycle of operation of these priorthermostats. The prior attempts to design a thermostat actuator bladewmch would eliminate the foregoing problems have generally resulted incomplicated designs involving compound bimetal blades, and the like,which have been found to be expensive to manufacture, operate andmaintain.

Accordingly, it is the purpose of this invention to provide an improvedactuator blade for use in thermostat assemblies which overcomes theforegoing problems. The blade in accordance with this invention is ofsimple design and can be manufactured with low unit cost without usingexpensive compound bimetals. Moreover, the geometric shape andproportions of the actuator blade of this invention allows thetemperature differential between operating cycles of a thermostatassembly to be closely controlled. The actuator blade further operatesto substantially minimize temperature overshoot or undershoot during thefirst cycle of operation.

Generally, the actuator blade in accordance with this invention isformed from thermostat metal and includes side legs which are spaced atone end and preferably joined at the other end. A compensating leg isextended between the spaced ends of the side legs, and defines the pointof actuation for the blade. The compensating leg serves to offsetundesirable control characteristics growing out of the wide temperaturegradient which normally exists along the active length of conventionalthermostat-actuating blades sensing rapidly heated or rapidly cooledsurfaces. The side legs of the blade include active portions whichrespond rapidly to the forced application of heat or cold to the bladeand thereby minimize temperature overshoot (if heating) and temperatureundershoot (if cooling) on the first cycle of operation. Moreover, thegeometric shape and proportion of the side legs and compensating leg ofthe blade results in a net movement of the bladeactuating point whichminimizes the temperature differential between successive heating orcooling cycles of the thermostat by quickening the making and breakingof the circuit being controlled by the thermostat.

Further features, objects and advantages of the present invention willbe more fully understood from the following description of an exemplaryembodiment, taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 iso plan view of a thermostat assembly incorporating the actuatorblade in accordance with the present invention;

FIG. 2 is a plan view of the actuator blade of the present inventionwhich is incorporated in the thermostat assembly illustrated in FIG. I;

FIG. 3 is an end elevational view of the actuator blade, as viewed alongthe line 3-3 in FIG. 2, with selected parts of the assembly shown inphantom in the normal positions assumed before the assembly is actuated;

FIG. 3A is a view similar to FIG. 3, illustrating an alternate designfor the push link in the thermostat assembly;

FIG. 4 is an elevational view of the thermostat assembly illustrated inFIG. I, showing the assembly components in their normal positions, withthe thermostat contracts closed, before the actuation of the assembly;

FIG. 5 is an end elevational view of the assembly as shown in FIG. 4; a

FIG. 6 is a side elevational view of the thermostat assembly, showingthe assembly components in the positions assumed after the assembly isactuated by an initial application of heat, and the blade has notattained uniform temperature in all of its parts.

FIG. 7 is an end elevational view of the assembly as shown in FIG. 6;

FIG. 8 is a side elevational view of the thermostat assembly, showingthe components of the assembly in the positions assumed after the heatapplied to the assembly has caused all of the parts of the blade toattain approximately the same temperature; and

FIG. 9 is an end elevational view of the thermostat assembly as shown inFIG. 8.

EXEMPLARY EMBODIMENT The improved thermostatic actuator blade embodyingthe advantages and features of the present invention is generallyindicated by the reference numeral I0 in the drawings. The blade 10 ismade of a suitable thermostat metal and is responsive to the applicationof heat. The preferred form of the blade I0 is made to have a unitaryconstruction by stamping the blade from a single sheet of the thermostatmetal. The blade 10 can be incorporated in a suitable thermostatassembly, such as the assembly illustrated in the drawings, to closelycontrol the temperature of devices such as flat irons, table appliances,copying equipment, etc. More specifically, the blade 10 will operate inthe thermostat assembly 100 to minimize the first cycle temperatureovershoot and the temperature differential between operating cycles forthe device being controlled. The blade 10 also will operate to minimizetemperature undershoot when used with a thermostatic control assemblyfor a cooled appliance.

Referring to the drawings in more detail, the illustrated thermostatassembly 100 is a conventional friction-free, stacktype thermostat,similar to that described in U.S. Pat. No. 3,221,124, issued on Nov. 30,I965, to Charles S. Mertler. Of course, it will be appreciated by thoseskilled in the art that the blade 10in accordance with this inventioncan be utilized with other forms of thermostat assemblies, includingsnap-acting types, to control the temperature of heated or cooledappliances.

The illustrated assembly 100 includes a heat collector I02 positioned atthe bottom of a stack of insulators 104. The heat collector I02 is madefrom a heat-conductive material, and is positioned in contact with thesurface of the appliance A for which the temperature is beingcontrolled. A cantilevered base 106 is positioned on the top of thestack of insulators I04 and projects a predetermined distance to theside of the insulator stack. Electrical terminals 112 and 113 aremounted on the assembly I00 between adjacent insulators 104 and areelectrically insulated from the hollow fastening rivet 108. The hollowrivet I08, formed either as a separate or integral part of heatcollector I02, is used to firmly join the heat collector I02, theinsulators 104, the electrical terminals I12 and 113, the contact blades114 and 116, and the base 106 in the stacked arrangement. Further, theassembly 100 can be firmly mounted on the appliance A by extending ascrew 110, or other suitable fastener, through the interior of thehollow rivet 100, or by providing a suitably shaped heat collector forother means of securing to appliance A.

The thermostat assembly 100 also includes an upper contact blade 114 anda lower contact blade 116. As illustrated in FIG. 4, the blades 114 and116 are positioned directly below the base 106, and extend apredetermined distance transversely from the stack of insulators 104, inthe same direction as the base 106. One end of the blade 114 ispositioned between adjacent insulators 104 in electrical contact withthe terminal 112, and one end of the blade 116 is positioned, in asimilar manner, in electrical contact with the terminal 113. Thisarrangement spaces the contact blades 114 and 116 a predetermineddistance apart. Further, the ceramic insulators 104 electricallyinsulate the blades 114 and 116 and terminals 112 and 113 from the heatcollector 102, the rivet 108 and the appliance A.

In addition, the free ends of the contact blades 114 and 116 carryopposed contact points 118 and 120, respectively. The contact points 118and 120 operate in the conventional manner to close the circuit betweenthe terminals 112 and 1 13 when the points are in contact, and to breakthe circuit between the terminals when the points are separated.

The assembly 100 also includes an adjusting screw 122, to permit thetemperature of appliance A to be preset within a given temperaturerange. To accomplish this, the screw 122 carries an insulating tip 124which extends through an aperture in the upper contact blade 114 andengages and positions the lower blade 116, which is otherwise biasedupward. Adjustment of the screw 122 thus changes the position of thelower contact blade 116 with respect to the blade 114, and determinesthe temperature at which the contact points 118 and 120 will separate. Asuitable stop 126 can be arranged on the base 106 adjacent the screw 122and a matching lug 123 attached to the adjusting screw for limiting therotation of adjustment for the screw 122 within a predetermined range.

In the illustrated embodiment, the actuator blade is positioned in thethermostat assembly 100 so as to extend beneath the contact blades 114and 116. One end of the blade 10 defines a substantial surface area 11which is fixed between the lowermost insulator 104 and the heatcollector 102 of the assembly. This arrangement places surface area 11of the blade 10 in direct heat-conductive relationship with theappliance A through the heat-conductive relationship with the applianceA through the heat collector 102. The outer free end of the actuatingblade 10 is extended below the contact blades 114 and 116 so that theblade 10 has a predetermined free length which can respond to a changein temperature in the appliance A. Metallic Washer 128 is mounted in thestack of insulators 104 on the top side of the fixed end of the blade 10to accurately define the free length of the blade 10.

As illustrated in FIGS. 3 and 4, the thermostat assembly 100 alsoincludes a push link 130 which is formed from ceramic or other suitableinsulating material. The upper end of the link 130 projects through anaperture 115 provided in the upper contact blade 114. The aperture 115is dimensioned to freely receive the link 130, and stabilizes the linkfrom excessive horizontal movement in the assembly. The upper portion ofthe link 130 also includes shoulders 131 which engage with the lowersurface of the contact blade 114 during operation of the assembly.Further, the main portion of the link 130 projects through an aperture117 in the bottom contact blade 116. Lower shoulders 132 are verticallyarranged on the link 130 to remain clear of the lower surface of thebottom contact blade 116 during the operation of the assembly 100, andto assure electrical spacing between blade 10 and blade 116 during anypossible conditions of adjustment or operation of the assembly 100. Thelower portion of the link 130 also projects through an aperture 32provided in the blade 10, and seats upon a pair of nibs 34 on the blade10. As clearly illustrated in FIG. 3, the link 130 and the othercomponents of the assembly are arranged so that the shoulders 131 on thelink are positioned slightly below or touching the contact blade 114before the initial actuation of the assembly. and clearance ismaintained between shoulders 132 and contact blade 116 before or duringactuation.

FIG. 3A illustrates a modified push link 1300 for use in the thermostatassembly 100. Like the above-described link 130, the modified link 130afunctions to transmit the motion of the actuating blade 10 to the uppercontact blade I14 and to assure electrical spacing between the actuatingblade 10 and the contact blade 116. The link 1304 is modified to have agenerally H-shaped configuration, and the adjacent portions of thecontact blades 114 and 116 are modified to receive the link.

Thus, the contact blade 114 is modified to have a pair of apertures 1150for receiving the upper end portions of the link 130 a, and a roundednib 115!) is provided on the blade 114 between the apertures 115a forengagement with the link 1300. The upper center portion of the link 1304is provided with a rounded shoulder 1310 which engages with the nib115b. The rounded configuration of the nib 115b and the shoulder 131aassures that the link 1300 and upper contact blade 114 will engage withsubstantially point contact. The lower contact blade 116 also ismodified to include a large aperture 117a for receiving the centralportion of the link a.

As illustrated in FIG. 3A, the blade 10 is also modified for use withthe push link 131a. The compensating leg 30 is provided with a pair ofaligned apertures 32a for receiving the H- shaped lower portion of thelink 1300. The central portion of the compensating leg 30 is furtherprovided with a raised, rounded nib 34a which engages with a roundedshoulder 35 provided on the lower central portion of the link 1310. Bythis arrangement, the compensating leg 30 of the blade 10 and the link131a will engage with substantially point contact.

Thus, the construction of the push link 1300, as shown in FIG. 3A,provides a link which has substantially two-point contact between theupper contact blade 114 and the actuating blade 10. Due to suchconstruction of the link 130a, the operation of the thermostat assembly100 will be essentially unaffected by slight misalignment of the link,or by the orientation of the assembly 100 in a position other thanhorizontal.

In the illustrated embodiment, the actuator blade 10 in accordance withthis invention is arranged in the assembly 100 with its low-expansionside defined by the top of the blade, and its high-expansion sidedefined by the bottom of the blade. As indicated in FIG. 2, one end ofthe blade 10 is provided with an aperture 12 for receiving the rivet 108of the assembly 100, as described above. The remaining portion of theblade 10 is formed to define a pair of diverging side legs 20 and acompensating leg 30 which extends transversely between the spaced freeends of the legs 20. The angle of divergency for the side legs 20 isapproximately l2 from the blade centerline. in the illustratedembodiment. Of course, it will be appreciated that this divergency canbe varied to adapt the blade 10 to the physical limitations ofparticular installations and to provide the compensating leg 30 with thedesired length and operating characteristics.

In the preferred form of the blade 10, the side legs 20 are formed bycutting a notch 21 from the center of the sheet material from which theblade is stamped. The central notch 21 divides the blade into the twoside legs 20, and reduces the width of the portion of the blade whichreceives the initial heat from the appliance A. The notch 21, generallyV- or U-shaped in configuration, thereby reduces the amount of bladematerial which must be heated and allows the initial heat to saturatethe area 11 of each side leg 20 very rapidly. The notch 21 also reduceswarpage in the blade 10 by eliminating material which may otherwisereact to heat by deforming transversely across the blade centerline.

As seen in FIG. 2, each of the side legs 20 of the blade 10 includes aflat, active portion 22 of a predetermined length and a formed inactiveportion 24. The active portions 22 have a substantial cross-sectionalarea, and are adapted to respond quickly to the application of heat tothe blade 10 by deforming in the vertical plane as viewed in thedrawings. Since the highcxpamiion side of the blmetal is on the lowerside of the blade 10. heat will cause the blade 10 to deform upwardly inthis embndiment.

In contrast to the active leg portions 22. the inactive portions 24 ofthe blade are designed to be unresponsive to the application of heat tothe blade. As seen from FIG. 3, this is accomplished by forming theblade material upwardly at the end of the active leg portions 22 so thatthe portions 24 comprise stifiening flanges having cross-sectional areassubstantially less than the cross-sectional area of the connected activeleg portion 22. Thus, the inactive portions 24 of each side leg arerigid, and are incapable of deforming in response to the flow of heatfrom the side legs 20. The resulting reduced cross section of theinactive portions 24 also operates as a heat choke and slows the flow ofheat from the side legs 20 into the compensating leg 30.

As explained further below, this arrangement of the side legs 20 permitsthe side legs to respond rapidly to the application of heat bydeactivating a major portion of the free length of the blade 10, asdefined by the inactive leg portions 24. The rapid response of the sidelegs 20 to heat is facilitated further by the concentration of the heatin the active leg portions 22 as a result of the heat-choking action ofthe reduced leg portions 24. Of course, the cross section of theinactive leg portions 24 can be selected to suit the particularrequirements of the appliance or the like under control.

The compensating leg 30 of the blade 10 is joined to the side legs 20 atthe outer extremities of the inactive leg portions 24. in theillustrated embodiment, the leg 30 is integral with the side legs 20,and likewise has the thermostat metal arranged with the low-expansionside on the top, and the high-expansion side is on the bottom. Thereduced cross section of the inactive leg portions 24 assure that thecompensating leg 30 will receive heat from the side legs 20 slowly asthe blade 10 becomes saturated.

Further, the arrangement of the leg 30 transversely across the ends ofthe side legs 20, with the high-expansion side of the thermostat metalon the bottom, will cause the leg 30 to deform downwardly in response toheat. After the initial heating cycle, this deformation of the leg 30,causing points of actuation 34 to move downward in a direction oppositefrom the upward movement of the side legs 20, thus will "compensate" forthe additional deformation of the side legs 20, as the side legs becomesaturated by moving the points of actuation 34 (or 34a) downwardlythrough a predetermined distance.

The length of the compensating leg 30 is selected to provide the blade10 with the desired amount of movement upon saturation by the heatflowing from the side legs 20. Since a longer bimetallic strip requiresmore time to saturate with heat than a shorter strip and results infurther physical movement upon saturation, it is evident that anincrease in the length of the leg 30 will increase the amount of suchdownward compensating movement, and a decrease in the length of the legwill correspondingly decrease the amount of movement. Of course, thecharacteristics of the leg 30 also can be changed to suit particularapplications by forming the leg 30 from a thermostat metal strip whichhas the desired characteristics of heat conductivity and movement.

The configuration of the compensating leg 30 also can be selected toadapt the blade 10 to a particular installation. In the illustratedembodiment, the leg 30 is shaped and arranged so that its centralportion along the centerline of the blade is raised. The point ofactuation for the leg 30, where the leg engages with and transmitsmovement to the link 130, is thereby raised so that the link 130 willnot interfere with the surface of the appliance A. As further indicatedin FIG. 2, the central portion of the leg 30 is also widened tostrengthen the leg adjacent the link aperture 32. The end portions ofthe leg 30, where the leg is joined to the inactive portions 24 of theside legs 20, are narrowed to delay the saturation of the leg 30 bypartially choking the flow of heat to the leg 30 from the side legs 20.The narrow end portions of the leg 30 further minimize twisting orspherical deformation of the leg 30 and thereby assure that thecompensating movement of the leg 30 will be substantially linear.

The various features and advantages of the actuator blade 10 inaccordance with this invention will be apparent from a description ofthe operation of the blade in the thermostat assembly to control thetemperature of the heating appliance A. Of course, it will beappreciated by those skilled in the art that the operation of the blade10 to control the temperature of a cooled appliance would be similar. Inan appliance wherein the actuation of a thermostat such as the assembly100 was induced by cooling rather than heating, the positioning of thethermostat metal iorrnlng the blade 10 would be reversed, e.g., thelow-expansion side of the bimetal would be on the bottom of the blade.However, the blade movement induced by a temperature change would be thesame as described below.

As illustrated in FIGS. 3-5 under normal conditions, before theapplication of heat to the appliance A, as controlled by thermostatassembly 100, the contact blades 114 and 116 are arranged to close thecontact points 118 and 120. The circuit between the terminals "2 and 113of the assembly is thereby completed so that heat may be applied to theappliance A by directing an electrical current through the terminals.The adjusting screw 122 is set so that the contacts 118 and willseparate and break the circuit when the surface of the appliance. A hasreached a predetermined temperature. As seen in H08. 3 and 4, theactuator blade 10 is undeformed under these normal unheated conditionsand supports the point of actuation for the leg 30 in an initialposition which places the shoulders 131 and 132 on the link slightlybelow the contact blades 114 and l 16, respectively.

As heat is applied to the appliance A, the heat is transmitted throughthe heat collector 102 directly to the blade 10. Because of thegeometric shape and proportions of the blade 10, the heat quickly flowsinto the active portions 22 of each of the blade side legs 20.Accordingly, when the appliance A has reached a predeterminedtemperature, the blade 10 will be deformed by the heat, with thegreatest curvature occurring in the side leg portions 22 adjacent to theheat collector 102, due to the natural temperature gradient as heatflows from heat collector 102 toward the blade extremities. The blade 10thereby will move quickly upward from the normal position illustrated inFIGS. 4 and 5 into a raised position, such as illustrated in FIGS. 6 and7. During this first cycle of operation of the thermostat 100, inactiveportions 24 of the blade legs 20 choke the passage of heat flowing fromthe active portions 22 of the blade and thereby accelerate thesaturation of the leg portions 22. The rigidity of the leg portions 24further prevents that portion of the legs from deforming in response tothe flow of heat from the blade portions 22. This arrangement minimizesfurther movement of the side legs 20 as the heat continues to flowthrough the side legs after the initial opening ofthe contacts 118 and120.

In addition, the configuration of the blade 10 slows the flow of heatfrom the inactive'portions 24 of the side arms 20 to the compensatingleg 30 during the initial heating cycle. The compensating leg 30 of theblade does not deform to any appreciable extent during the initialapplication of heat to the blade, and the movement of the points ofactuation of blade 10 is initially controlled by the active portions 22of the side legs 20.

Due to the configuration and design of the blade 10, the active portions22 of the side legs 20, which are immediately adjacent the source ofheat, will respond to a temperature change before the heat sheets thecompensating leg 30. Thus, the initial application of the heat to thethermostat 100 will quickly deform the blade 10 and cause the free endof the blade 10 to swing upwardly toward the contact blades 114 and 116.This upward movement of the blade 10 in turn forces the link 130upwardly and engages the shoulders 13] of the link with the uppercontact blade 114. The link 130 is further arranged so that the lowershoulders 132 do not engage the lower contact blade 116 during thismovement of the link. The

movement of the blade 10 is thereby transmitted to the blade 114 andraises the blade 11 to break the contact 118 away from the contact 120.

The blade 10 in accordance with this invention therefore is capable ofresponding quickly to the initial application of heat to swing the freeend of the blade through a predetermined arc and break the circuit ofthe thermostat before the heat has dissipated throughout the blade. Theblade thus minimizes first cycle temperature overshoot, and therebypermits the heat to the appliance A to be cut off during the first cycleat a temperature which closely corresponds to the cutoff temperature ofsucceeding cycles.

As well known by those skilled in the art, the heat applied to theactuator blade 10 continues to dissipate throughout the blade after thecontacts 118 and 120 are separated, until the side legs are heatsaturated. As this saturation occurs, the side legs 20 of the blade willcontinue to deform and will raise the blade 10 into a further elevatedposition, such as illustrated in FIGS. 8 and 9. The saturation of theside legs 20 thus continues the separation of the contacts 118 and [20after the circuit has been broken by the initial application of heat tothe blade 10.

ln conventional actuator blades, this additional separation of thecontacts requires the blade to cool for an undesirably delayed timebefore the contacts can be closed to start the succeeding heating cyclefor the appliance. This delay in conventional actuator blades in turnresults in an undesirably large temperature differential between cycles.in contrast to conventional blades, the blade 10 in accordance with thisinvention minimizes the amount of this additional deformation, uponsaturation of the side legs 20, by providing the inactive portions 24 onthe free end of each side leg. Since these leg portions 24 cannot deformin response to heat, the continued deformation of the side legs will beminimized as the heat dissipates throughout the blade. The amount ofcooling needed of the blade which must occur between the first andsecond heat cycles, as well as between succeeding cycles is thusappreciably reduced. The temperature differential between operatingcycles for the thermostat 100 is thereby minimized.

Moreover, the compensating leg 30 included on the blade 10 also acts topermit close control of the temperature differential between cycles, bycompensating for the additional deformation of the side legs 20. Becauseof the arrangement of the leg 30, the heat applied to the side legs 20will ultimately flow into the leg 30 and cause the leg 30 to deformdownwardly in a direction opposite from the deformation of the legs 20from the position such as illustrated in FIGS. 6 and 7 to a lowerposition, as illustrated in FIGS. 8 and 9. Thus, as the heat saturatesthe blade to, the leg 30 compensates for the additional upwarddeformation of the legs 20, which otherwise would tend to separate thecontact points I18 and 120 further, by returning the actuating point ofthe blade toward its initial position.

The net movement of the contact point 118 resulting from saturation ofthe blade 10 is thus substantially reduced in comparison to the totalmovement occurring in conventional blades, due to saturation ofconventional blades after the contacts of the thermostat open. As seenby comparing FIGS. 6 and 7 to FIGS. 8 and 9, the blade 10 is preferablydesigned so that the compensating downward movement of the actuatingpoints of leg 30 spaces the contacts "8 and I20 approximately the samedistance apart as when the circuit was broken by the initial upwardmovement of the side legs 20. Hence, the thermostat contacts 118 and 120engage again very rapidly. The blade 10 will thus start the subsequentoperating cycle for the assembly 100 when the temperature of theappliance A drops to a set level, and the temperature differentialbetween cycles will be minimized.

The blade 10 operates in a similar manner in the succeeding cycles ofthe thermostat assembly I00. After the blade 10 has cooled suflicientlyto return the contacts 118 and I20 into engagement, the appliance A willreceive heat to initiate the second heating cycle. As heat is conductedto the blade 10, the active portions 22 of the side legs 20 againsaturate very rapidly and deform upwardly. The legs 20 thereby raise thelink 130 to break the circuit between the contacts 118 and I20. Then, asthe heat is distributed throughout the blade 10, the compensating leg 30eventually becomes saturated, and

deforms downwardly. The downward movement of the leg 30 thereforecompensates for the increased upward movement of the side legs 20 andreturns the contact point 118 into position for beginning the nextheating cycle.

It is apparent from the above description that the blade 10 effectivelyquickens the separation of the contacts 118 and 120, and the breaking ofthe circuit of the thermostat 100, especially during the first cycle,when the appliance A is heated from a cold temperature. The bladetherefore reduces first cycle overshoot. The blade 10 also reduces theeffective temperature differential on succeeding cycles of operation, byincreasing the speed of making and breaking the engagement between thecontacts 118 and 120.

It is further apparent from the above description that the blade 10 canbe proportioned and the assembly calibrated to operate in a normalfashion as a temperature control and still act as a rate-of-rise limitcontrol" by responding to extreme rates of temperature rise as may occurdue to abnormal conditions such as in a water-heating appliance when itruns dry or is started dry inadvertently. Typical examples arecoffeemakers, or hot-beverage vendors or dispensers.

Although the invention has been described with a certain degree ofparticularity and in the heating mode, it should be understood that thepresent disclosure has been made only by way of example. Consequently,numerous changes in the details of construction and the combination andarrangement of components as well as the possible modes of utilization,will be apparent to those familiar with the art, and may be resorted towithout departing from the spirit and scope of the invention as claimed.

What I claim is:

l. in a thermostat assembly having a pair of movable contact means formaking and breaking an electrical circuit and thereby controlling theapplication of heat to a medium, the improvement comprising an actuatorblade formed from multilayered thermally responsive material, said bladecomprismg:

a pair of spaced side legs adapted at one end to define a substantialblade area for connection to a source of heat and spaced at the otherend;

a compensating crossleg bridging transversely across the spaced ends ofsaid side legs, said crossleg having said layers arranged in the samerelative position as said side legs, and defining a point of actuationfor said blade between said side legs; and

means linking said point of actuation to one of said contact means fortransmitting the motion of said point to said one contact means;

each of said side legs defining an active leg portion adjacent saidblade area formed from segments of said material having a substantialcross-sectional area and thereby adapted to receive heat quickly fromsaid source and an inactive leg portion positioned between said activeportion and said compensating leg adapted to be substantiallyunresponsive to the application of heat thereto and further having areduced cross-sectional area relative to said active leg portions tochoke the flow of heat from the connected active leg portion;

whereby said leg portions cooperate to concentrate the initial heatapplied to said blade in said active portions of said side legs so thatsaid active portions respond quickly to said initial heat to move saidpoint of actuation from an initial position through a predetermineddistance and thereby break said contact means with minimum temperatureovershoot; and

said compensating leg being adapted to receive heat from said side legsthrough said inactive leg portions and to respond to the flow of heattherethrough by returning said point of actuation a predetermineddistance toward said initial position;

whereby said compensating leg acts to bring said contact means togetherand compensates for the additional movement of said side legs induced byheat saturation of said active leg portionsand thereby accelerates themaking of said contact means and reduces the temperature differentialbetween succeeding heat cycles of said thermostat assembly.

2. A thermostat assembly in accordance with claim I wherein said linkingmeans comprises a member which extends between said point of actuationand said one contact means and which engages said point and said onecontact means at single locations, so that the operation of saidthermostat assembly is not adversely affected by misalignment of saidone contact means and said blade.

An actuator for use in a thermostat assembly comprising a blade formedfrom multiple layers of thermally responsive material, said bladeincluding:

a pair of spaced side legs adapted at one end to define a blade portionfor connection to a source of heat and transversely spaced at the otherend; and

a compensating cross leg joined to said side legs and transverselybridging across said spaced ends, said compensating crossleg having saidlayers arranged in the same relative position as said side legs, anddefining a point of actuation for said blade between said side legs;

each of said side legs defining an active leg portion formed fromsegments of said material having a substantial crosssectional area andthereby adapted to deform quickly in response to the flow of heat intosaid blade to move said point of actuation a predetermined distance froman initial position of said point;

each of s id legs further including an inactive portion positionedbetween said active portion and compensating leg and comprising portionsformed from said material having a reduced cross-sectional area relativeto said active leg portions and thereby being adapted to delay the flowof heat from said active portions to said compensating leg;

said compensating leg being adapted to receive heat from said side legsand to respond to such heat fiow by deforming with respect to said sidelegs to return said point of actuation a predetermined distance towardsaid initial position;

whereby said compensating leg acts to compensate for additional movementof said point induced by heat saturation of said side legs.

4. An actuator for use in a thermostat assembly comprising a bladeformed from multiple layers of thermally responsive material, said bladeincluding:

a pair of spaced side legs adapted at one end to define a said side legsbeing spaced to provide said compensating leg with a substantial lengthand each of said side legs defining an active leg portion formed fromsegments of said material having a substantial cross-sectional area andthereby adapted to deform quickly in response to the flow of heat intosaid blade to move said point of actuation a predetermined distance froman initial position of said point;

- each of said side legs further including an inactive portionpositioned between said active portion and compensating leg andcomprising substantial rigid leg portions having a reducedcross-sectional area relative to said active leg portions and therebybeing substantially unresponsive to the application of heat thereto andadapted to choke the flow of heat from said active portions to saidcompensating leg;

said compensating leg being adapted to receive heat from said side legsand to respond to such heat flow by deforming with respect to said sidelegs to return said point of actuation a predetermined distance towardsaid initial position;

whereby said compensating leg acts to compensate for additional movementof said point induced by heat saturation of said side legs occurringafter the initial heating cycle.

5. An actuator for use in a thermostat assembly comprising a bladeformed from multiple layers of thermally responsive material, said bladeincluding:

a pair of spaced side legs adapted at one end to define a blade portionfor connection to a source of heat and transversely spaced at the otherend; and

a compensating cross leg formed from a segment of said material joinedto said side legs transversely across said spaced ends. saidcompensating crossleg having said layers arranged in the same relativeposition as said side legs and defining a point of actuation for saidblade between said side legs;

said side legs diverging toward said spaced ends to provide saidcompensating leg with a substantial length and each of said side legsdefining an active leg portion formed from segments of said materialhaving a substantial crosssectional area and thereby adapted to deformquickly in response to the flow of heat into said blade to move saidpoint of actuation a predetermined distance from an initial position ofsaid point;

each of said side legs further including an inactive portion positionedbetween said active portion and compensating leg and comprising rigidflange portions formed from said material having a reducedcross-sectional area relative to said active leg portions and therebybeing substantially unresponsive to the application of heat thereto andadapted to choke the flow of heat from said active portions to saidcompensating leg;

said compensating leg being adapted to receive heat from said side legsand to respond to such heat flow by deforming with respect to said sidelegs to return said point of actuation a predetermined distance towardsaid initial position;

whereby said compensating leg acts to compensate for additional movementof said point induced by heat saturation of said side legs.

6. in a thermostat assembly having a pair of movable contacts for makingand breaking an electrical circuit and thereby controlling theapplication of heat to a medium, the improvement comprising an actuatorblade formed from multilayered thermally responsive material, said bladecomprising:

a pair of diverging side legs adapted at one end to define a substantialblade area for connection to a source of heat and spaced at the otherend;

a compensating leg formed from a substantially flat portion of saidmaterial integral with said side legs and extended transversely betweenthe spaced ends of said side legs and further defining a point ofactuation for said blade between said side legs; and

means linking said point of actuation to one of said contacts fortransmitting the motion of said point to said contact;

each of said side legs defining an active leg portion adjacent saidblade area comprising substantially flat segments of said materialhaving a substantial cross-sectional area and adapted to receive heatquickly from said source; each of said side legs further defining aninactive leg portion adjacent said compensating leg formed from a rigidflange portion of said material having 'a reduced cross-sectional arearelative to said active leg portions and adapted to be substantiallyunresponsive to the application of heat thereto and to choke the flow ofheat from the connected active leg portion;

whereby said leg portions cooperate to concentrate the initial heatapplied to said blade in said active portions of said side legs so thatsaid active portions respond quickly to said initial heat to move saidpoint of actuation from an initial position through a predetermineddistance and stantial temperature gradient between the controlled mediumand the compensating leg at said point of actuation occurring during theinitial heating cycle. and further compensates for the additionalmovement of said side legs induced by heat saturation of said active legportions. whereby said blade accelerates the making of said contacts andreduces the temperature differential of the heated medium during theheating cycles.

1. In a thermostat assembly having a pair of movable contact means formaking and breaking an electrical circuit and thereby controlling theapplication of heat to a medium, the improvement comprising an actuatorblade formed from multilayered thermally responsive material, said bladecomprising: a pair of spaced side legs adapted at one end to define asubstantial blade area for connection to a source of heat and spaced atthe other end; a compensating crossleg bridging transversely across thespaced ends of said side legs, said crossleg having said layers arrangedin the same relative position as said side legs, and defining a point ofactuation for said blade between said side legs; and means linking saidpoint of actuation to one of said contact means for transmitting themotion of said point to said one contact means; each of said side legsdefining an active leg portion adjacent said blade area formed fromsegments of said material having a substantial cross-sectional area andthereby adapted to receive heat quickly from said source and an inactiveleg portion positioned between said active portion and said compensatingleg adapted to be substantially unresponsive to the application of heatthereto and further having a reduced cross-sectional area relative tosaid active leg portions to choke the flow of heat from the connectedactive leg portion; whereby said leg portions cooperate to concentratethe initial heat applied to said blade in said active portions of saidside legs so that said active portions respond quickly to said initialheat to move said point of actuation from an initial position through apredetermined distance and thereby break said contact means with minimumtemperature overshoot; and said compensating leg being adapted toreceive heat from said side legs through said inactive leg portions andto respond to the flow of heat therethrough by returning said point ofactuation a predetermined distance toward said initial position; wherebysaid compensating leg acts to bring said contact means together andcompensates for the additional movement of said side legs induced byheat saturation of said active leg portions and thereby accelerates themaking of said contact means and reduces the temperature differentialbetween succeeding heat cycles of said thermostat assembly.
 2. Athermostat assembly in accordance with claim 1 wherein said linkingmeans comprises a member which extends between said point of actuationand said one contact means and which engages said point and said onecontact means at single locations, so that the operation of saidthermostat assembly is not adversely affected by misalignment of saidone contact means and said blade.
 3. An actuator for use in a thermostatassembly comprising a blade formed from multiple layers of thermallyresponsive material, said blade including: a pair of spaced side legsadapted at one end to define a blade portion for connection to a sourceof heat and transversely spaced at thE other end; and a compensatingcross leg joined to said side legs and transversely bridging across saidspaced ends, said compensating crossleg having said layers arranged inthe same relative position as said side legs, and defining a point ofactuation for said blade between said side legs; each of said side legsdefining an active leg portion formed from segments of said materialhaving a substantial cross-sectional area and thereby adapted to deformquickly in response to the flow of heat into said blade to move saidpoint of actuation a predetermined distance from an initial position ofsaid point; each of said legs further including an inactive portionpositioned between said active portion and compensating leg andcomprising portions formed from said material having a reducedcross-sectional area relative to said active leg portions and therebybeing adapted to delay the flow of heat from said active portions tosaid compensating leg; said compensating leg being adapted to receiveheat from said side legs and to respond to such heat flow by deformingwith respect to said side legs to return said point of actuation apredetermined distance toward said initial position; whereby saidcompensating leg acts to compensate for additional movement of saidpoint induced by heat saturation of said side legs.
 4. An actuator foruse in a thermostat assembly comprising a blade formed from multiplelayers of thermally responsive material, said blade including: a pair ofspaced side legs adapted at one end to define a blade portion forconnection to a source of heat and transversely spaced at the other end;and a compensating crossleg formed from a segment of said materialjoined to said side legs transversely across said spaced ends, saidcompensating crossleg having said layers arranged in the same relativeposition as said side legs, and defining a point of actuation for saidblade between said side legs; said side legs being spaced to providesaid compensating leg with a substantial length and each of said sidelegs defining an active leg portion formed from segments of saidmaterial having a substantial cross-sectional area and thereby adaptedto deform quickly in response to the flow of heat into said blade tomove said point of actuation a predetermined distance from an initialposition of said point; each of said side legs further including aninactive portion positioned between said active portion and compensatingleg and comprising substantial rigid leg portions having a reducedcross-sectional area relative to said active leg portions and therebybeing substantially unresponsive to the application of heat thereto andadapted to choke the flow of heat from said active portions to saidcompensating leg; said compensating leg being adapted to receive heatfrom said side legs and to respond to such heat flow by deforming withrespect to said side legs to return said point of actuation apredetermined distance toward said initial position; whereby saidcompensating leg acts to compensate for additional movement of saidpoint induced by heat saturation of said side legs occurring after theinitial heating cycle.
 5. An actuator for use in a thermostat assemblycomprising a blade formed from multiple layers of thermally responsivematerial, said blade including: a pair of spaced side legs adapted atone end to define a blade portion for connection to a source of heat andtransversely spaced at the other end; and a compensating cross legformed from a segment of said material joined to said side legstransversely across said spaced ends, said compensating crossleg havingsaid layers arranged in the same relative position as said side legs anddefining a point of actuation for said blade between said side legs;said side legs diverging toward said spaced ends to provide saidcompensating leg with a substantial length and each of said side legsdefining an active leg portion formed from segments of sAid materialhaving a substantial cross-sectional area and thereby adapted to deformquickly in response to the flow of heat into said blade to move saidpoint of actuation a predetermined distance from an initial position ofsaid point; each of said side legs further including an inactive portionpositioned between said active portion and compensating leg andcomprising rigid flange portions formed from said material having areduced cross-sectional area relative to said active leg portions andthereby being substantially unresponsive to the application of heatthereto and adapted to choke the flow of heat from said active portionsto said compensating leg; said compensating leg being adapted to receiveheat from said side legs and to respond to such heat flow by deformingwith respect to said side legs to return said point of actuation apredetermined distance toward said initial position; whereby saidcompensating leg acts to compensate for additional movement of saidpoint induced by heat saturation of said side legs.
 6. In a thermostatassembly having a pair of movable contacts for making and breaking anelectrical circuit and thereby controlling the application of heat to amedium, the improvement comprising an actuator blade formed frommultilayered thermally responsive material, said blade comprising: apair of diverging side legs adapted at one end to define a substantialblade area for connection to a source of heat and spaced at the otherend; a compensating leg formed from a substantially flat portion of saidmaterial integral with said side legs and extended transversely betweenthe spaced ends of said side legs and further defining a point ofactuation for said blade between said side legs; and means linking saidpoint of actuation to one of said contacts for transmitting the motionof said point to said contact; each of said side legs defining an activeleg portion adjacent said blade area comprising substantially flatsegments of said material having a substantial cross-sectional area andadapted to receive heat quickly from said source; each of said side legsfurther defining an inactive leg portion adjacent said compensating legformed from a rigid flange portion of said material having a reducedcross-sectional area relative to said active leg portions and adapted tobe substantially unresponsive to the application of heat thereto and tochoke the flow of heat from the connected active leg portion; wherebysaid leg portions cooperate to concentrate the initial heat applied tosaid blade in said active portions of said side legs so that said activeportions respond quickly to said initial heat to move said point ofactuation from an initial position through a predetermined distance andthereby break said contacts with minimum temperature overshoot; and saidcompensating leg being adapted to receive heat from said side legsthrough said inactive leg portions and to respond to the flow of heattherethrough by returning said point of actuation a predetermineddistance toward said initial position; whereby said compensating legacts to move said contacts toward a closed position and compensates forthe substantial temperature gradient between the controlled medium andthe compensating leg at said point of actuation occurring during theinitial heating cycle, and further compensates for the additionalmovement of said side legs induced by heat saturation of said active legportions, whereby said blade accelerates the making of said contacts andreduces the temperature differential of the heated medium during theheating cycles.